1. Field of the Invention
The present invention relates generally to a crosstalk compensating circuit for the crosstalk among a plurality of signal transmission paths, and is directed more particularly to a crosstalk compensating circuit suitable for use in a stereo pickup cartridge, an FM stereo receiver a multi-channel tape recorder and so on.
2. Description of the Prior Art
Stereophonic reproduction of a sound signal may adversely be affected when crosstalk occurs from one channel to another channel. Crosstalk, may give rise, for example, to left and right expansions of a reproduced sound, localization of the reproduced sound and residual sound effects and may effect sharpness and brightness of the reproduced sound.
Prior art crosstalk compensating circuits for a stereophonic signal is disclosed in Japanese Utility Model Registration No. 590,061 entitled "Crosstalk adjusting apparatus for a stereophonic signal", the invention of which has been assigned to the assignee of the present application.
The above prior art crosstalk adjusting apparatus will be now described with reference to FIG. 1 which shows the adjusting apparatus schematically. With this prior art apparatus, the reverse phase sides of signal transmission paths R and L are coupled by a suitable impedance element Z and the other sides thereof are connected by a lead wire. In this case, if a crosstalk is given between the reverse phase sides of the signal transmission paths R and L, a sum signal S = L + R (where L is the left signal and R the right signal) of the stereophonic signal decreases and its ratio to a difference signal D = L - R also decreases to increase the stereophonic sense.
As noted above, prior art crosstalk compensating circuit, are designed on the assumption that the left and right crosstalk components are same in amplitude and polarity. Accordingly, adequate crosstalk compensation cannot be obtained if the left and right crosstalk components are different in amplitude and/or polarity and possibly also in phase.
One of the elements used in a stereophonic reproduction system which is apt to produce substantial crosstalk, is a mechanical-electrical transducer, i.e. pickup cartridge.
Measurements of crosstalk produced in the transducer, have shown that the amplitudes of the left and right crosstalk components are not always same. For example, when a changeable cartridge is attached to a support, such as a pickup arm, obliquely from its normal position, the geometric relation between the sound groove of a record disc and the signal-generation system of the pickup cartridge is adversely affected. In such case, if the above oblique or inclined angle is taken as .theta., a crosstalk corresponding to tan .theta. is produced and an amplitude difference may thus exist between the left and right crosstalk components which exceeds 6 dB. In the most serious case, the left and right crosstalk components are of opposed polarity.
As to the phase of crosstalk components, it has been ascertained that the phase of crosstalk component of a cartridge whose separation is about 20 dB is about 0.degree. or 180.degree., while that of a cartridge whose separation is about 30 dB is substantially .+-.90.degree.. It will thus be apparent that the prior art crosstalk compensating circuit which presupposes crosstalk components of equal amplitude and polarity will not reduce crosstalk where the crosstalk components are of unequal amplitude and different polarity and possibly also of different phase.